Yes, it requires regular payment, from the SaaS perspective, since the cost is a monthly expense, adopting a subscription model is understandable. This pricing was inspired by https://jsoncrack.com/. May I ask, is there anything on the pricing page that is hard to understand?
Generally, when you download a dev tool to run a tool on your own machine that is not pre-packaged software, it does not have a subscription cost. That is likely the source of confusion.
It’s unclear what service requires the expense on your side that justifies a monthly cost. I think explaining those benefits on the pricing page would help you a great deal.